The role of a novel subgroup of chitinases in fungal biology

Chitin, second most commonly occurring compound on earth, is the main structural component of invertebrate exoskeletons and fungal cell walls. In nature it has a faster turnover time than cellulose and chitin degrading enzymes, secreted by microorganisms, are of major importance for its recycling. Fungal genomes contain between 10 and 25 different chitinases, indicating that fungi have developed a complex chitinolytic enzyme system. Fungal chitinases have different metabolic roles including (i) degradation of exogenous chitin, (ii) cell wall remodelling during hyphal growth and (iii) competition and defence against other fungi and arthropods, which has developed into active attack mechanisms on other fungi (mycoparasitism) by e.g. Hypocrea/Trichoderma species or insects (entomopathogenic fungi). In a recent genomic study of chitinases in the soil fungus Hypocrea/Trichoderma we identified a novel subgroup of fungal chitinases, which was named subgroup C. Members of this subgroup are large proteins containing several carbohydrate binding domains, namely LysM and chitin binding domains that are not present in other fungal chitinases. In our study we showed that the first cloned chitinase from subgroup C in fungi, Hypocrea atroviridis chi18-10, showed a differential, highly selective regulation in contrast to other chitinases. The aim of this project is to study the novel subgroup C of fungal chitinases and elucidate the function and importance of these chitinases in fungi, with emphasis on mycoparasitic Hypocrea/Trichoderma species. In this project we will study the evolution and biodiversity of subgroup C chitinases in ascomycetous fungi with specialized habitats and analyze the regulation of these chitinases by different growth conditions. Further, we will investigate the involvement of subgroup C chitinases in the different chitin-degrading processes as implicated above. The properties of the carbohydrate binding domains (chitin-binding domains and LysM domains), a characteristic feature of subgroup C chitinases, will be analyzed biochemically in more detail with respect to their carbohydrate binding properties. Using this multidisciplinary approach of bioinformatic, genetic and biochemical methods, this project will contribute greatly to the understanding of fungal chitinases and will help to elucidate diversity of the potential roles of these fungal enzymes in the ecosystem.

Chitin, second most commonly occurring compound on earth, is the main structural component of invertebrate exoskeletons and fungal cell walls. In nature it has a faster turnover time than cellulose and chitin degrading enzymes, secreted by microorganisms, are of major importance for its recycling. Fungal genomes contain between 10 and 25 different chitinases, indicating that fungi have developed a complex chitinolytic enzyme system. Fungal chitinases have different metabolic roles including (i) degradation of exogenous chitin, (ii) cell wall remodelling during hyphal growth and (iii) competition and defence against other fungi and arthropods, which has developed into active attack mechanisms on other fungi (mycoparasitism) by e.g. Hypocrea/Trichoderma species or insects (entomopathogenic fungi). In a recent genomic study of chitinases in the soil fungus Hypocrea/Trichoderma we identified a novel subgroup of fungal chitinases, which was named subgroup C. Members of this subgroup are large proteins containing several carbohydrate binding domains, namely LysM and chitin binding domains that are not present in other fungal chitinases. In our study we showed that the first cloned chitinase from subgroup C in fungi, Hypocrea atroviridis chi18-10, showed a differential, highly selective regulation in contrast to other chitinases. The aim of this project is to study the novel subgroup C of fungal chitinases and elucidate the function and importance of these chitinases in fungi, with emphasis on mycoparasitic Hypocrea/Trichoderma species. In this project we will study the evolution and biodiversity of subgroup C chitinases in ascomycetous fungi with specialized habitats and analyze the regulation of these chitinases by different growth conditions. Further, we will investigate the involvement of subgroup C chitinases in the different chitin-degrading processes as implicated above. The properties of the carbohydrate binding domains (chitin-binding domains and LysM domains), a characteristic feature of subgroup C chitinases, will be analyzed biochemically in more detail with respect to their carbohydrate binding properties. Using this multidisciplinary approach of bioinformatic, genetic and biochemical methods, this project will contribute greatly to the understanding of fungal chitinases and will help to elucidate diversity of the potential roles of these fungal enzymes in the ecosystem.